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The mechanisms of the decline in coronary heart disease mortality are not fully elucidated. In particular, little is known about the trends in severity of myocardial infarction, which may have contributed to the mortality decline. This study examines indicators of myocardial infarction severity including Killip class, electrocardiogram descriptors, and peak creatine kinase values in a population-based, myocardial infarction incidence cohort to test the hypothesis that the severity of myocardial infarction declined over time. Between 1983 and 1994, 1,295 incident cases of myocardial...

The mechanisms of the decline in coronary heart disease mortality are not fully elucidated. In particular, little is known about the trends in severity of myocardial infarction, which may have contributed to the mortality decline. This study examines indicators of myocardial infarction severity including Killip class, electrocardiogram descriptors, and peak creatine kinase values in a population-based, myocardial infarction incidence cohort to test the hypothesis that the severity of myocardial infarction declined over time. Between 1983 and 1994, 1,295 incident cases of myocardial infarction (mean age, 67 (standard deviation, 6) years; 43% women) occurred in Olmsted County, Minnesota. The median time between the onset of symptoms and presentation was 1.9 (interquartile range, 3.9) hours and declined over time (p = 0.018), while the use of reperfusion therapy increased. Over time, the hemodynamic presentation of patients did not change appreciably, but the proportion of persons with ST-segment elevation declined as did the occurrence of Q waves and peak creatine kinase values. These secular trends, which were largely independent from the time to first electrocardiogram and reperfusion therapy, indicate a decline in the severity of myocardial infarction over time. Am J Epidemiol 2002;156:246–53.